Google tests a new interface for the chat logs saved in Gmail. The new interface shows profile images and hides the regular buttons and menus that are displayed for almost all messages and conversations. For some reason, Google removed buttons like “move to inbox”, “delete”, “labels”, the “more” drop-down, the “reply” button and the associated menu. Timestamps are only displayed when you mouse over a chat line.
There’s a new “resume chat” button and a “delete messages history” button that triggers this warning: “Deleting the history will permanently delete all messages in this chat conversation. The messages will not go to the Trash. You will still receive messages that are sent after this action.”
I don’t see this new interface in my Gmail account, but maybe you have more luck. You can find Gmail’s chat history here: https://mail.google.com/mail/#chats. The interface should only look different for recent conversations, so you can still see the old UI for the other chat conversations.